Structural Health Monitoring (SHM) is vital to ensuring the integrity and longevity of civil structures, as well as providing data and design feedback for the modification or retrofit of existing structures, or the construction of new structures. By observing the performance and state of a structure through SHM techniques, much information can be obtained which quantify how a structure responds to its real world environment and its present state of health. Although computer simulations and analyses can predict a structural response to various loading conditions and environmental parameters, it is also important to monitor the performance of the structure during its construction and throughout its life. SHM gives key information regarding structural condition and capabilities, provides feedback to help validate or invalidate the design models, highlights factors neglected in the modeling process and provides insight into the condition and lifespan of structures. SHM also provides invaluable information for determining maintenance schedules and upkeep requirements.
However, even with all the benefits SHM has to offer, the size, complexity, and accessibility of the structures themselves often makes monitoring difficult or impossible with conventional human-based monitoring techniques. The use of mobile robots to deploy sensors and gather data in SHM applications provides alternatives to human-based systems and greatly increases the feasibility of employing SHM in many hazardous, confined, or inaccessible structures or structural components.
Perhaps the most significant challenge to creating a robot platform for SHM applications is the diversity and variability of the structures themselves. Aside from creating small, specialized robots designed to travel across a single structure, or even a single aspect of a structure, utilization of robotics in SHM has been extremely limited. However, by creating a robotic platform which has the ability to traverse a wide variety of configurations and geometric complexities, robots can be applied to SHM of many different structures with only a few robotic platform configurations.
Many civil structures are made from ferromagnetic materials, predominantly steel. Being of major importance to civil infrastructure, monitoring of the health of these systems is critical. Typical examples of structures which can benefit from SHM include bridges, coffer dams, pipelines, power stations, transmission towers, water towers, radio towers, construction sites, skyscrapers, offshore oil platforms, and many others.
Employing sensor nodes and networks for gathering data for SMH is not a new idea. Numerous specialized robots have been constructed for specific structures; however, these robots are generally limited in mobility and cannot be used on a variety of structure configurations. Instead, they are designed for single applications to a specific structure. Such robots include utility pole climbers and I-beam traversing units. A robot known as “The Robotic Inspector,” or RobIn, was developed at the Intelligent Robotics Lab at Vanderbilt University to inspect manmade structures. RobIn is highly mobile and versatile, but is restricted by limited payload areas and a power cord. Visual/Inspection Technologies Inc. has a unit called “SPOT” that utilizes movable cameras for pipe inspection and has developed other robotic systems. Although SPOT can travel into areas where humans cannot reach, it still requires a human operator and is specific to piping applications.
Other robots for pipe specific applications have been developed at North Carolina State University. Their proposed use is to crawl through pipes that remain intact after a building collapse and search for survivors trapped in the wreckage. They can also be used to detect gas leaks. However, a robot platform which has the capability to traverse a wide variety of structural and geometric configurations would add considerable versatility to a robotic SHM application. To create such a robot, a novel technique for attachment to the structure is needed to avoid designs based upon tracks or specialized mechanical gripping.
Biologically inspired robots have been widely praised as having many features desirable in an automated platform, and rely on locomotion techniques which have endured millennia of testing and refinement through the evolutionary process. Creating a biologically inspired robot results in an effective platform of locomotion, however the means by which the robot physically attaches to the structure is still in question. A promising advancement in this field recently has been the development of a gecko-foot like material which utilizes van der Waals forces to cling to smooth surfaces, in the same way as the gecko lizard is able to walk up a glass window. This material can grip non-magnetic surfaces, but disengaging its grip remains problematic. Also, its use and reuse on rough or scaly surfaces is severely limited. Other attachment efforts have utilized electromagnets, and have even included non-switchable permanent magnet tracks for the inspection of underground storage tanks.